1. Field of the Disclosure
The present invention relates generally to detecting a change of an output voltage of an isolated power converter, and more specifically, the invention relates to sensing a ringing voltage from a bias winding of an isolated power converter to detect a change in output voltage.
2. Background
Many electrical devices such as cell phones, personal digital assistants (PDA's), laptops, etc. are powered by a source of relatively low-voltage dc power. Power is typically delivered through a wall outlet as high-voltage ac power. A device generally referred to as a switching power converter is typically used to transform the high-voltage ac power to low-voltage dc power. In certain applications, electrical devices may require a constant output voltage and/or a minimum operating voltage delivered from a power converter. In operation, a power converter may use a controller to control a switch that transfers energy from the input side to the output side of the power converter in order to maintain a constant voltage at the output of the power converter.
One characteristic of a power converter may be that it provides galvanic isolation between the input and the output of the power converter, meaning there is no dc current path to allow current to flow from the input side to the output side of the power converter. In one example, a power converter may include an energy transfer element such as a coupled inductor that galvanically isolates the input side from the output side of the power converter. During operation, a power converter may regulate the output voltage at the output of the power converter by using a controller that is coupled to a sensor to provide feedback from the output of the power converter in order to regulate the output voltage. More specifically, the controller may regulate output voltage at the output of the power converter by controlling a switch to turn on and off in response to the feedback information from the sensor to transfer energy pulses through the isolation element to the output from a source of input power such as a power line.
One type of power converter may be a primary side control power converter. This type of power converter uses a feedback mechanism that is indirectly coupled to the output side of a galvanically isolated power converter. In one example, a primary side control power converter may use a bias winding that is magnetically coupled to the output winding to sense an output voltage.